Liquid crystal display

ABSTRACT

A liquid crystal display mainly includes two substrates processed for vertical alignment and a liquid crystal having a negative dielectric constant anisotropy sealed between the two substrates. An array of slits is provided on pixel electrodes formed on one substrate. A light-shielding matrix and an array of protrusions is provided on the other substrate. Each of the first protrusions has a main body being arranged substantially in a zigzag pattern and in parallel to one another. The slits and the main bodies of the first protrusions are arranged alternately. The liquid crystal display is characterized in that the first protrusions have a plurality of breaks formed within the area of the light-shielding matrix.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a liquid crystal display(LCD), and more particularly to a multi-domain vertically aligned (MVA)LCD having specific protrusion pattern for use in a one drop fill (ODF)process.

2. Description of the Related Art

Liquid crystal display mainly comprises two oppositely positioned firstand second substrates and a liquid crystal layer interposedtherebetween. U.S. Pat. No. 5,263,888 discloses a one drop fill (ODF)process comprising the steps of applying an adhesive onto the entireperiphery of the first substrate, dropping the liquid crystal materialto the first substrate, superposing the second substrate upon the firstsubstrate and pressing the substrates until a gap between the substratesreaches a predetermined value (typically 3-10 micrometers), and curingthe adhesive. In the step of pressing the substrates, the liquid crystalmaterial spreads to fill the space between the substrates therebyforming the liquid crystal layer.

Vertically-aligned (VA) LCD is a mode using a negative liquid crystalmaterial and vertical alignment films. Comparing with the twistednematic (TN) LCD, the vertically-aligned (VA) LCD provides highercontrast, higher response speed, and excellent viewing anglecharacteristics for white display and black display. However, the VA LCDstill has a critical drawback of a narrow viewing angle. This poses aproblem that the application of the VA LCD is limited.

European Patent Publication Number 0884626-A2 discloses a multi-domainvertically aligned (MVA) LCD having domain regulating means forimproving viewing angle performance thereof. Typically, the domainregulating means is realized by providing slits on the pixel electrodesof the TFT substrate and providing protrusions on the common electrodeof the CF (color filter) substrate. The pattern of the protrusions iscontinuous and the protrusions are arranged in substantially the sameway in all pixels. The protrusions typically have a height of around1-2μ. For an MVA LCD with a smaller cell gap (3-3.9 μm) design, thespacing between the protrusions and the TFT substrate is about 2-2.9 μm.If the MVA LCD is manufactured by the aformentioned ODF process, bubbleis prone to be entrapped between the protrusions in a continuouspattern. In such a case, it may be found that an insufficient degree ofspreading of the liquid crystal material will occur during the step ofpressing the substrates thereby creating bubbles between theprotrusions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a multi-domainvertically aligned (MVA) LCD having discontinuous regulating means thatovercomes or at least reduces the above-mentioned problems of the priorart.

To achieve the above listed and other objects, the LCD according to thepresent invention comprises a first substrate and a second substrateprocessed for vertical alignment, a liquid crystal being sandwichedbetween the first and second substrates, and discontinuous regulatingmeans provided on at least one of the first and second substrates. Theliquid crystal layer includes liquid crystal molecules aligning in adirection generally perpendicular to a principal surface of said firstsubstrate when no substantial electric field is applied to said liquidcrystal layer. The discontinuous regulating means regulates orientationof the liquid crystal layer such that the liquid crystal molecules arealigned obliquely when a voltage is applied so that the orientation willinclude a plurality of directions within each pixel. Since theregulating means is formed in a discontinuous pattern, air trappedbetween the first and second substrates can be easily vented through theregulating means, thereby significantly reducing the occurring rate ofbubbles.

According to one embodiment of the present invention, the discontinuousregulating means is realized by providing an array of first protrusionsand slits wherein each of the first protrusions has a plurality ofbreaks formed therein. The first protrusions are formed on the secondsubstrate wherein each of the first protrusions has a main body beingarranged substantially in a zigzag pattern and in parallel to oneanother. The slits are provided on the pixel electrodes provided on thefirst substrate in a manner that the slits and the main bodies of thefirst protrusions are arranged alternately. The breaks of the firstprotrusions allow air trapped between the first protrusions to be easilyvented therethrough, thereby significantly reducing the occurring rateof bubbles. Furthermore, during the step of pressing the substrates inthe ODF process, the breaks of the first protrusions allows the droppedliquid crystal material to be spread more evenly such that the liquidcrystal material will completely fill the cavity formed between the twosubstrates. However, since the pattern of the first protrusions isdiscontinuous, the orientation of the liquid crystal molecules isdisordered at the edges of the breaks. This results in disclinationgenerating around the edges of the breaks. Therefore, all of the breaksmay be designed to have a predetermined size in order to achieve goodair ventilation while minimizing disclination. Alternatively, all of thebreaks may be formed within the area of the light-shielding matrixformed on the second substrate thereby significantly masking thedeteriorated display quality such as light leakage due to disclination.

Typically, the second substrate may have a plurality of gate linesformed parallel to one another and a plurality of data lines formedparallel to one another vertically to the gate lines. The pixelelectrodes have first edges parallel to the gate lines and second edgesparallel to the data lines. The light-shielding matrix has a pluralityof columns extending along the data lines and a plurality of rowsextending along the gate lines. Therefore, all of the breaks may bedesigned to be located within the area of the rows and/or the columns ofthe light-shielding matrix such that none of the first protrusionsextends across the rows and/or the columns of the light-shieldingmatrix.

Preferably, the first protrusions may have a plurality of first branchesformed at positions facing the first edges of the pixel electrodes and aplurality of second branches formed at positions facing the second edgesof the pixel electrodes. In this embodiment, the difference between thedirectors (i.e., the average direction of the long axes of the LCmolecules) of the LC molecules around the branches and slits issignificantly reduced down to at most 45 degrees. This significantlysuppresses disclination occurring at the border between the slits andthe pixel electrode edges, thereby avoiding display defects due to thedisclination.

According to another embodiment of the present invention, the secondsubstrate further comprises a plurality of second protrusions formedinside one channel defined by two first branches extending from the mainbodies of adjacent first protrusions and the first and secondsubstrates.

According to still another embodiment of the present invention, thesecond substrate further comprises a plurality of third protrusions eachformed at a location close to one channel defined by two first branchesextending from the main bodies of adjacent first protrusions and thefirst and second substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

FIG. 1 a is a plan view of a portion of an MVA LCD showing specificprotrusion pattern according to a first embodiment of the presentinvention;

FIG. 1 b is a plan view of the MVA LCD of FIG. 1 a showing specificprotrusion and slit pattern;

FIG. 2 is a plan view of a portion of an MVA LCD showing specificprotrusion pattern according to a second embodiment of the presentinvention;

FIG. 3 is a plan view of a portion of an MVA LCD showing specificprotrusion pattern according to a third embodiment of the presentinvention;

FIG. 4 is a plan view of a portion of an MVA LCD showing specificprotrusion pattern according to a fourth embodiment of the presentinvention;

FIG. 5 is a plan view of a portion of an MVA LCD showing specificprotrusion pattern according to a fifth embodiment of the presentinvention; and

FIG. 6 is a partial cutaway view of a vertically-aligned (VA) LCDaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a multi-domain vertically aligned (MVA)LCD having discontinuous regulating means for use in liquid crystalinjecting process such as one drop fill (ODF) process. The LCD accordingto the present invention comprises a first substrate and a secondsubstrate processed for vertical alignment and a liquid crystal beingsandwiched between the first and second substrates. The discontinuousregulating means is provided on at least one of the first and secondsubstrates. The liquid crystal layer includes liquid crystal moleculesaligning in a direction generally perpendicular to a principal surfaceof said first substrate when no substantial electric field is applied tosaid liquid crystal layer. The discontinuous regulating means regulatesorientation of the liquid crystal layer such that the liquid crystalmolecules are aligned obliquely when a voltage is applied so that theorientation will include a plurality of directions within each pixelthereby improving viewing angle performance. Since the regulating meansis formed in a discontinuous pattern, air trapped between the first andsecond substrates can be easily vented through the regulating means,thereby significantly reducing the occurring rate of bubbles.

As shown in FIG. 6, the LCD mainly comprises a first substrate 102 and asecond substrate 104. The surfaces of the substrates are processed forvertical alignment. A liquid crystal 130 having a negative dielectricconstant anisotropy is sealed between the two substrates. The MVA LCD ofthe present invention is preferably a thin-film transistor LCD.Typically, the first substrate 102 is referred to as a color filter (CF)substrate because color filters 102 a are formed, while the secondsubstrate 104 is referred to as a TFT substrate. Usually, spacers (notshown) are formed between the substrates for defining a cell gap betweenthe substrates.

FIGS. 1 a and 1 b show a portion of an MVA LCD 100 with discontinuousregulating means realized by providing specific protrusion and slitpattern according to a first embodiment of the present invention. Thefirst substrate 102 has a light-shielding matrix 101 (not shown in FIG.1 b), for example a black matrix, formed thereon. The second substrate104 is provided with a plurality of parallel gate lines 104 a, aplurality of parallel data lines 104 b perpendicular to the gate lines104 a, and a plurality of thin film transistors (TFTs) and pixelelectrodes 120 (not shown in FIG. 1 a) formed like a matrix at theintersections between the gate lines 104 a and data lines 104 b. Thepixel electrode 120 has first edges 120 a parallel to the gate lines 104a and second edges 120 b parallel to the data lines 104 b. The LCD 100is formed with a plurality of protrusions 130 and slits 140 (not shownin FIG. 1 a) for regulating the orientation of the liquid crystal suchthat the alignment of liquid crystal molecules is induced by applicationof a voltage to include a plurality of directions. By virtue oforientating the liquid crystal molecules into a plurality of mutuallydifferent directions, the viewing angle the LCD 100 can be greatlyincreased. The protrusions 130 are arranged in parallel to one anotheron the first substrate. Each protrusion 130 has a main body 130 a beingbent substantially in a zigzag pattern. The slits 140 are provided onthe pixel electrodes 120. As shown in FIG. 1 b, the slits 140 and themain bodies 130 a of the protrusions are arranged alternately.

The protrusions 130 of the MVA LCD 100 have a plurality of breaks 130 bsuch that air trapped between the protrusions 130 can be easily ventedthrough the breaks 130 b, thereby significantly reducing the occurringrate of bubbles. Furthermore, during the step of pressing the substratesin the ODF process, the breaks 130 b of the protrusions 130 allows thedropped liquid crystal material to be spread more evenly such that theliquid crystal material will completely fill the cavity formed betweenthe two substrates. However, since the pattern of the protrusions 130 isdiscontinuous, the tilting direction of the liquid crystal molecules dueto the protrusions 130 becomes disordered at the edges of the breaks 130b. This results in disclination generating around the edges of thebreaks 130 b. Therefore, all of the breaks 130 b may be designed to havea predetermined size in order to achieve good air ventilation whileminimizing disclination. Alternatively, all of the breaks 130 b may beformed within the area of the light-shielding matrix 101 therebysignificantly masking the deteriorated display quality such as lightleakage due to disclination.

As shown in FIG. 1 a, the light-shielding matrix 101 has a plurality ofrows 101 a extending along the gate lines 104 a and a plurality ofcolumns 101 b extending along the data lines 104 b. All of the breaks130 b are designed to be located within the area of the rows 101 a ofthe light-shielding matrix such that none of the protrusions 130 extendsacross the rows 101 a. Alternatively, the protrusions of the presentinvention may have breaks 130 c (see FIG. 5) all located within the areaof the columns 101 b of the light-shielding matrix such that none of theprotrusions extends across the columns 101 b of the light-shieldingmatrix. All of the breaks may be designed to be located within the areaof the rows and the columns of the light-shielding matrix such that noneof the protrusions extends across the rows and the columns of thelight-shielding matrix.

Generally speaking, when the liquid crystal display is only providedwith the slits 140 and the main bodies 130 a of the protrusions bent inzigzag, some particular area within the pixel appear darkened. Thechange of the orientation of the liquid crystal in the darkening areaturns to become slow in response to the voltage applied. This reducesthe contrast and the response speed, thereby deteriorating the displayquality. This is due to the fact that the inclination of liquid crystalmolecules influenced by the electric field near the edges 120 a, 120 bof the pixel electrode 120 (see FIG. 1 b) is considerably different fromthat caused by the slits 140 in the darkening area. Therefore, as shownin FIG. 1 b, the protrusions 130 preferably have a plurality of firstbranches 130 d formed at positions facing the first edges 120 a of thepixel electrodes 120 and a plurality of second branches 130 e formed atpositions facing the second edges 120 b of the pixel electrodes 120. Inthis embodiment, the difference between the directors (i.e., the averagedirection of the long axes of the liquid crystal molecules) of theliquid crystal molecules around the branches 130 d, 130 c and the slits140 is significantly reduced down to at most 45 degrees. Thissignificantly suppresses disclination occurring at the border betweenthe domain formed by the edges of the pixel electrode 120 and the domainformed by the slits 140, thereby avoiding display defects due to thedisclination.

FIG. 2 shows the pixel region of an MVA LCD 200 according to a secondembodiment of the present invention wherein the pixel electrodes 120 andthe slits 140 are not shown. This LCD 200 includes a plurality ofprotrusions 132 formed inside one channel defined by two first branches130 d extending from the main bodies 130 a of adjacent protrusions 130and the substrates 102, 104 (not shown). During the step of pressing thesubstrates in the ODF process, the protrusions 132 slow down the flowrate of the dropped liquid crystal material through the aformentionedchannel defined by the first branches 130 d.

FIG. 3 shows the pixel region of an MVA LCD 300 according to a thirdembodiment of the present invention wherein the pixel electrodes 120 andthe slits 140 are not shown. This LCD 300 includes a plurality ofprotrusions 134 formed at a location close to the left opening of theaformentioned channel. During the step of pressing the substrates in theODF process, the protrusions 134 slow down the flow rate of the droppedliquid crystal material through the aformentioned channel.

FIG. 4 shows the pixel region of an MVA LCD 400 according to a fourthembodiment of the present invention wherein the pixel electrodes 120 andthe slits 140 are not shown. This LCD 400 includes a plurality ofprotrusions 136 formed at a location close to the right opening of theaformentioned channel. During the step of pressing the substrates in theODF process, the protrusions 136 slow down the flow rate of the droppedliquid crystal material through the aformentioned channel.

Next, the process for forming the aformentioned protrusions will bedescribed as follows. A photoresist is coated on the surface thereof,transferred a predetermined pattern (referring to the protrusion patternshown in FIGS. 1-5), and then developed to form the protrusions 130,132, 134, 136. This process is easily carried out by using conventionaltechniques. Additionally, the slits 140 can be formed simultaneouslywith the pixel electrodes 120 by utilizing conventional process.

Although the invention has been explained in relation to its preferredembodiment, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1-15. (canceled)
 16. A liquid crystal display, comprising: a firstsubstrate and a second substrate processed for vertical alignment; aliquid crystal layer sandwiched between the first and second substrates,the liquid crystal layer including liquid crystal molecules aligning ina direction substantially perpendicular to a principal surface of saidfirst substrate when no substantial electric field is applied to saidliquid crystal layer; a pair of gate lines and a pair of data linesdefines a pixel area and a pixel electrode formed within the pixel area,an array of first protrusions and a light-shielding matrix disposed onthe second substrate, each of the first protrusions having a main bodybeing arranged substantially in a broken zigzag pattern, the brokenzigzag pattern being broken by a plurality of breaks all formed withinan area of the light-shielding matrix, and a plurality of secondprotrusions provided on the second substrate, each of the secondprotrusions being formed at a location close to one of the broken zigzagpattern of the first protrusions.
 17. The liquid crystal display asclaimed in claim 16, wherein the first substrate comprises an array ofslits provided on the pixel electrodes; the main bodies of the firstprotrusions are arranged substantially in parallel to one another; andthe slits and the main bodies of the first protrusions are arrangedalternately.
 18. The liquid crystal display as claimed in claim 16,wherein: the light-shielding matrix has a plurality of columns extendingalong the data lines and a plurality of rows extending along the gatelines, and wherein none of the main bodies of the first protrusionsextends across the rows of the light-shielding matrix.
 19. The liquidcrystal display as claimed in claim 16, wherein: the light-shieldingmatrix has a plurality of columns extending along the data lines and aplurality of rows extending along the gate lines, and wherein none ofthe main bodies of the first protrusions extends across the columns ofthe light-shielding matrix.
 20. The liquid crystal display as claimed inclaim 16, wherein: the light-shielding matrix has a plurality of columnsextending along the data lines and a plurality of rows extending alongthe gate lines, and wherein none of the main bodies of the firstprotrusions extends across the columns and the rows of thelight-shielding matrix.
 21. The liquid crystal display as claimed inclaim 16, further comprising a plurality of branches extending from thebreaks of the first protrusions, wherein a plurality of channels areeach defined as a space between two adjacent branches; and the pluralityof second protrusions are formed inside said channels.
 22. A liquidcrystal display, comprising: a first substrate and a second substratefacing each other; a liquid crystal layer sandwiched between the firstand second substrates; an array of protrusions disposed on one of thefirst and second substrates, each of the protrusions having a main bodyarranged substantially in a broken zigzag pattern, the broken zigzagpattern being broken by a plurality of breaks, and a plurality ofbranches extending from the breaks of the protrusions, wherein aplurality of channels are each defined as a space between two adjacentbranches.
 23. The liquid crystal display as claimed in claim 22,wherein: the first substrate comprises a plurality of pixel electrodes,and an array of slits on the pixel electrodes; the main bodies of theprotrusions are arranged substantially in parallel to one another; andthe slits and the main bodies of the first protrusions are arrangedalternately.
 24. The liquid crystal display as claimed in claim 32,further including: a light-shielding matrix disposed on the secondsubstrate, the light-shielding matrix having a plurality of columns anda plurality of rows, wherein none of the main bodies of the protrusionsextends across the rows of the light-shielding matrix.
 25. The liquidcrystal display as claimed in claim 22, further including: alight-shielding matrix disposed on the second substrate, thelight-shielding matrix having a plurality of columns and a plurality ofrows, wherein none of the main bodies of the protrusions extends acrossthe columns of the light-shielding matrix.
 26. The liquid crystaldisplay as claimed in claim 22, further including: a light-shieldingmatrix disposed on the second substrate, the light-shielding matrixhaving a plurality of columns and a plurality of rows, wherein none ofthe main bodies of the protrusions extends across the columns and therows of the light-shielding matrix.
 27. The liquid crystal display asclaimed in claim 22, wherein: the branches extend in the same direction.28. The liquid crystal display as claimed in claim 22 further including:a plurality of second protrusions formed near the channels.
 29. Theliquid crystal display as claimed in claim 22 further including: aplurality of second protrusions formed in the channels.
 30. A liquidcrystal display, comprising: a first substrate and a second substratefacing each other; a liquid crystal layer sandwiched between the firstand second substrates; an array of protrusions disposed on the secondsubstrates, each of the protrusions having a main body arrangedsubstantially in a broken zigzag pattern and extending in a firstdirection, wherein the broken zigzag pattern is broken by a plurality ofbreaks; a plurality of branches extending from the breaks of theprotrusions and in a second direction, wherein the second direction issubstantially perpendicular to the first direction; and a plurality ofchannels each being defined as a space between two adjacent branches.31. The liquid crystal display as claimed in claim 30, wherein: thefirst substrate comprises a plurality of pixel electrodes, and an arrayof slits on the pixel electrodes; the main bodies of the protrusions arearranged substantially in parallel to one another; and the slits and themain bodies of the protrusions are arranged alternately.
 32. The liquidcrystal display as claimed in claim 30, further including: alight-shielding matrix disposed on the second substrate, thelight-shielding matrix having a plurality of columns and a plurality ofrows, wherein none of the main bodies of the protrusions extends acrossthe columns of the light-shielding matrix.
 33. The liquid crystaldisplay as claimed in claim 30, further including: a light-shieldingmatrix disposed on the second substrate, the light-shielding matrixhaving a plurality of columns and a plurality of rows, wherein none ofthe main bodies of the protrusions extends across the columns and therows of the light-shielding matrix.
 34. The liquid crystal display asclaimed in claim 30, further including: a plurality of secondprotrusions formed near the channels.
 35. The liquid crystal display asclaimed in claim 30 further including: a plurality of second protrusionsformed in the channels.